The instant invention relates to relative position indication systems and more particularly to a position indication system which is operative with extremely high levels of accuracy and reliability for determining the relative positions between a pair of first and second members.
Relative position indication systems have generally been found to be essential to the effective operation of many types of devices, such as certain precision machine tools. For example, it has been found that it can often be extremely important to know the precise orientation and position of a workpiece relative to a tool holding system, as the position of the workpiece is changed relative to the tool holding system along either a linear or a rotational path while a machining operation is performed on the workpiece. However, while several types of both induction and optical position indication systems have been heretofore available for applications of this type, they have generally been found to be either unreliable or very costly.
The heretofore available induction position indication systems have generally comprised induction resolvers comprising pairs of aligned spaced plates having uniform rotary or linear cyclical precision windings thereon. A resolver of this type is generally operative by passing an alternating current flow through the windings on one of the plates thereof in order to induce a voltage in the windings on the other plate which is precisely related to the relative positions of the cyclical windings on the two plates. It has been found that it is possible to precisely determine the relative positions of the two plates of a device of this type within a single cycle, and it has been further found that by counting the number of cycles passing by a zero or initialized position on one of the plates as the relative positions of the plates are changed, it is possible to determine the overall relative positions of the two plates along a predetermined path of movement at any given instant. However, it has also been found that signal noise, interference, and/or momentary power interruptions can produce errors in the cycle count of a device of this type and that, as a result, while it is possible to reliably and accurately determine the relative positions of the plates of a device of this type within a single cycle, it is not always possible to reliably determine the overall relative positions of the plates based on a cycle count. In order to overcome this problem, some of the heretofore available induction resolvers have included initialization or reset signal generators for resetting the relative positions of the plates thereof to zero or initialized values whenever the plates thereof are moved through zero or initialized positions. However, these devices have been operative for resetting the overall relative positions between the plates thereof; and, as a result, they have often introduced fractional position errors. Other induction resolvers have included additional enlarged single cycle windings for determining the overall relative positions between the plates thereof. However, while these devices have generally been found to be effective, they have also been found to be relatively expensive.
The heretofore available optical position indication systems have generally comprised optical encoders of a type comprising a glass plate having a predetermined pattern of markings thereon, a light source and a light sensor which is operative for sensing the light from the light source as it is passed through the glass plate in order to determine the position of the glass plate. However, devices of this type have generally been found to be less accurate than induction resolvers, and they have generally been found to operate more slowly than induction resolvers.
The instant invention provides an effective position indication system which overcomes the disadvantages of many of the heretofore available position indication systems. Specifically, the instant invention provides a position indication system which is operative for determining the relative positions of a pair of first and second members as the first member is moved in either a positive or a negative direction along a predetermined path cf movement relative to the second member. More specifically, the system of the instant invention comprises a cyclical position sensor including a first portion which is securable in effectively fixed relation to a first member and a second portion which is securable in effectively fixed relation to a second member. The first portion includes means defining a predetermined number of sequential cycles thereon, one of which is designated as a zero cycle, and each of the cycles on the first portion is uniformly divided into a plurality of cycle segments. The second portion of the position sensor preferably also includes means defining a predetermined number of sequential cycles thereon, one of which corresponds to a zero position station, and the system is constructed so that sequential cycles on the first portion sequentially pass by the zero position station when the first portion is moved along a predetermined path of movement relative to the second portion. The system further comprises means responsive to the cycles on the first portion for determining the relative positions of the first and second portions within the cycle located at the zero position station at any given time and summing means for determining the sum total of the number of cycles passing by the zero position station in a positive direction minus the number of cycles passing by the zero position station in a negative direction. The system further comprises pulse generating means which is mounted in effectively fixed relation with either the first portion of the sensor or the second portion of the sensor and operative for generating pulse signals which indicate movement of the zero cycle past the zero position station and pulse sensing means which is mounted in effectively fixed relation with the other one of the first or second portions of the sensor and which is operative for sensing the pulse signals generated by the pulse generating means. The system still further comprises means responsive to the pulse sensing means for resetting the summing means to an initialized value without resetting the cycle positioning means each time the zero cycle passes by the zero position station.
In the preferred embodiment of the system of the instant invention, the cyclical position sensor comprises an induction resolver, and the first and second portions each have a predetermined number of cyclical precision windings thereon. The pulse generating means preferably comprises a pulse generator, and the pulse sensing means preferably comprises a pulse receiver. The pulse generator and the pulse receiver are preferably mounted in fixed positions relative to either the first portion of the position sensor or the second portion of the position sensor, and the pulse generating means preferably further comprises a selective interference plate which is mounted in a fixed position relative to the other one of the first or second portions of the cyclical position sensor. The interference plate is operative for selectively interfering between the pulse generator and the pulse receiver in order to selectively transmit pulse signals to the pulse receiver which correspond only to the zero cycle location. Further, the pulse generator is preferably operative for only producing a single pulse signal each time a cycle passes by the zero position station, and all of the pulse signals are preferably timed to occur at the same relative positions in the respective cycles thereof. Still further, each of the pulse signals preferably has a duration which causes it to extend over a distance corresponding to less than one cycle width as the first portion is moved relative to the second portion, and each pulse signal is preferably positioned to occur entirely within a single cycle.
Accordingly, it is seen that the position indication system of the instant invention represents a significant improvement over the heretofore available position indication systems. Specifically, the position indication system of the instant invention is operative for initializing or resetting the cycle count to zero each time the zero cycle passes by the zero position station so that cycle count errors resulting from interference, signal noise, and/or power interruptions, etc., are eliminated each time the zero cycle passes by the zero position station. However, since the system is operative for resetting only the cycle count rather than the overall relative position reading between the first and second portions of the position sensor, errors are not introduced into the relative positions of the first and second portions within a specific cycle. As a result, the system of the instant invention is operative for accurately determining the relative positions between a pair of first and second members within a single cycle, and it is also operative for accurately determining an overall cycle count.
Accordingly, it is a primary object of the instant invention to provide an effective and accurate relative position indication system.
Another object of the instant invention is to provide an induction resolver position indication system wherein the overall cycle count is updated each time the system passes through a predetermined zero orientation.
An even further object of the instant invention is to provide an induction resolver position indication system wherein the overall cycle count is updated without altering the relative position within a cycle each time the system passes through a predetermined zero orientation.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.